This invention is generally directed to squaraine compositions, and to processes for the preparation thereof. More specifically, the present invention is directed to unsymmetrical squaraine compositions containing (poly)alkoxyaryl substituents, which squaraines can be synthesized by cycloaddition-condensation processes, thereby avoiding the use of costly squaric acid as a reactant. In one embodiment of the present, invention there are provided unsymmetrical squaraine compositions containing (poly)methoxyphenyl substituents with improved xerographic properties, inclusive of high charge acceptance, low dark decay, high photosensitivity, and improved cyclic stability when these compositions are incorporated into photoconductive imaging members. Accordingly, in another embodiment of the invention of the present application there are provided imaging members with photoconductive layers comprised of the unsymmetrical squaraines illustrated herein, and charge or hole transport layers, especially those comprised of aryl amines, which members are sensitive to light in the wavelength region of from about 400 to about 1,000 nanometers. Therefore, the resulting members are responsive to visible light, and infrared illumination originating from laser printing apparatuses wherein, for example, gallium arsenide diode lasers are selected. The photoresponsive imaging members of the present invention can also, for example, contain situated between a photogenerating layer and a hole transporting layer, or situated between a photogenerating layer and a supporting substrate with a charge transport layer in contact with the photogenerating layer, a photoconductive composition comprised of the unsymmetrical squaraines illustrated herein.
Numerous different xerographic photoconductive members, including squaraines and processes thereof, are known, for example, a homogeneous layer of a single material such as vitreous selenium, or a composite layered device containing a dispersion of a photoconductive composition. An example of one type of composite xerographic photoconductive member is described, for example, in U.S. Pat. No. 3,121,006, wherein there are disclosed finely divided particles of a photoconductive inorganic compound dispersed in an electrically insulating organic resin binder. These members contain, for example, coated on a paper backing a binder layer containing particles of zinc oxide uniformly dispersed therein. The binder materials disclosed in this patent comprise a material such as polycarbonate resins, polyester resins, polyamide resins, and the like, which are incapable of transporting for any significant distance injected charge carriers generated by the photoconductive particles. Accordingly, as a result the photoconductive particles must be in a substantially continuous particle to particle contact throughout the layer for the purpose of permitting charge dissipation required for a cyclic operation. Thus, with the uniform dispersion of photoconductive particles described a relatively high volume concentration of photoconductor material, about 50 percent by volume, is usually necessary in order to obtain sufficient photoconductor particle to particle contact for rapid discharge. There are also known photoreceptor materials comprised of inorganic or organic materials wherein the charge carrier generating, and the charge carrier transport functions are accomplished by discrete contiguous layers. Additionally, layered photoreceptor materials are disclosed in the prior art, which include an overcoating layer of an electrically insulating polymeric material. Recently, there have been disclosed other layered photoresponsive devices including those comprised of separate generating layers, and transport layers as described in U.S. Pat. No. 4,265,990; and overcoated photoresponsive materials containing a hole injecting layer, overcoated with a hole transport layer, followed by an overcoating of a photogenerating layer; and a top coating of an insulating organic resin, reference U.S. Pat. No. 4,251,612. Examples of photogenerating layers disclosed in these patents include trigonal selenium, and phthalocyanines, while examples of transport layers include certain diamines as mentioned therein. Also, there is illustrated in U.S. Pat. No. 4,415,639, the disclosure of which is totally incorporated herein by reference, the use of known squaraine compositions, such as hydroxy squaraines, as a photoconductive layer in an infrared sensitive photoresponsive device. More specifically, there is described in this patent an improved photoresponsive device containing a substrate, a hole blocking layer, an optional adhesive interfacial layer, an inorganic photogenerating layer, a photoconductive composition capable of enhancing or reducing the intrinsic properties of the photogenerating layer, which photoconductive composition is selected from various squaraine compositions, including hydroxy squaraine compositions, and a hole transport layer. Other patents disclosing photoconductive devices with squaraines are U.S. Pat. Nos. 4,471,041; 4,486,520; 4,508,803; 4,507,480; 4,552,822; 4,390,610; 4,353,971; and 4,391,888.
Furthermore, there are illustrated in U.S. Pat. No. 4,624,904, the disclosure of which is totally incorporated herein by reference, photoconductive imaging members with unsymmetrical hydroxy squaraine compositions, and aryl amine hole transport layers. The aforementioned unsymmetrical squaraine compounds can be prepared, for example, by the initial preparation of an aryl cyclobutenedione intermediate, followed by the reaction thereof with a substituted aniline. More specifically, with respect to method A illustrated in the '904 patent, the aryl cyclobutenedione is prepared by heating with reflux at a temperature of from about 40.degree. to about 50.degree. C., depending on the solvent selected; about 20 millimoles to about 50 millimoles of substituted aniline; from about 60 millimoles to about 150 millimoles of dihalocyclobutenedione; and from about 100 milliliters to about 1,000 milliliters of a Fredal Craft solvent inclusive of, for example, carbon disulfide nitrobenzene or methylene chloride. This reaction is accomplished in the presence of from about 200 to about 900 millimoles of a catalyst such as aluminum chloride, and the resulting substituted aniline is reacted with a hydroxy substituted aniline in the present of an aliphatic alcoholic solvent. Subsequent to separation, there are obtained the desired unsymmetrical squaraine compounds of the formula as detailed on page 8, beginning at line 10, for example. Also, in copending application U.S. Ser. No. 557,795 there are described photoresponsive imaging members containing unsymmetrical squaraines comprised by forming a mixture of squaraic acid, a primary alcohol, a first tertiary amine, and a second tertiary amine.
Furthermore, there are disclosed in several patents processes for preparing squaraine compositions. For example, in U.S. Pat. No. 4,524,220 there is illustrated a squaraine process by the reaction of squaric acid, and an aromatic aniline in the presence of an aliphatic amine. Also, in U.S. Pat. No. 4,524,219 there is described a process for the preparation of squaraines by the reaction of an alkyl squarate, and an aniline in the presence of aliphatic alcohol, and an optional acid catalyst. Moreover, disclosed in U.S. Pat. No. 4,524,218 are processes for the preparation of squaraines by the reaction of squaric acid with an aromatic amine, and a composition selected from the group consisting of phenols, and phenol squaraines, which reaction is accomplished in the presence of an aliphatic alcohol, and an optional azeotropic catalyst. Other processes for preparing squaraines are illustrated in U.S. Pat. No. 4,525,592, wherein there is described the reaction of a dialkyl squarate, and an aniline in the presence of an aliphatic alcohol, and an acid catalyst.
Although the above squaraines, and processes thereof are suitable for their intended purposes, there continues to be a need for other photoconductive unsymmetrical squaraines. Additionally, and more specifically there remains a need for simple, economical processes for preparing certain unsymmetrical squaraine compositions with stable properties, which when incorporated into photoconductive devices result in reduced dark decay characteristics, and increased charge acceptance values as compared to substantially similar squaraine compositions. Moreover, there remains a need for processes that enable the preparation of unsymmetrical squaraines wherein the use of costly squaraic acid component reactants are avoided. In addition, there remains a need for photoconductive imaging members with certain stable electrical characteristics, that is for example the aforementioned imaging members are electrically stable for over 50,000 xerographic imaging cycles. In addition, imaging members with the aforementioned unsymmetrical squaraines of the present invention are sensitive to a broad range of wavelengths, including visible and infrared light, such as of from about 400 to about 850 nanometers, enabling such members to be useful in electrophotographic imaging and printing processes, including processes wherein diode lasers are selected.